High capacity easy release extended use adhesive devices

ABSTRACT

The invention provides novel devices, systems, designs, materials and fabrication methods that enable high-load capacity, easy release, and suitable for extended/repeated use in a variety of applications.

PRIORITY CLAIMS AND RELATED APPLICATIONS

This application claims the benefit of priority from PCT/US11/57309,filed Oct. 21, 2011, which claims the benefit of priority from U.S.Provisional Application Ser. No. 61/405,544, filed Oct. 21, 2010, theentire content of each of which is incorporated herein by reference forall purposes.

GOVERNMENT RIGHTS

The United States Government has certain rights to the inventionpursuant to Grant No. N66001-08-C-2054 from the Department of Navy tothe University of Massachusetts.

TECHNICAL FIELD OF THE INVENTION

The invention generally relates to designs, devices, materials andmethods useful for weight-bearing. More particularly, the inventionrelates to designs, devices, systems, materials and fabrication methodsthat provide adhesive devices that are high-load bearing, easy release,and suitable for extended/repeated use in a variety of applications.

BACKGROUND OF THE INVENTION

Adhesive materials that can support high capacity loads havetraditionally been sought. Pressure sensitive adhesives (PSAs) areself-adhesives that form a bond when pressure is applied to marry theadhesive with the adherend. Typically, no solvent, water, or heat isnecessary to activate or stimulate the adhesive to perform. ConventionalPSAs have found use in pressure sensitive tapes, labels, note pads,automobile interior trims, and a wide variety of other products. Therehas been continued effort among the scientific community to create andproduce synthetic materials and devices that mimic the performance ofanimals, such as geckos, in Nature.

PSAs typically rely on ubiquitous surface force interactions, such asvan der Waals forces, to transfer stress across an interface. Pressuresensitive adhesives can adhere to a surface because the adhesive is softenough to flow, or wet, the adherend. The adhesive needs to be hardenough to resist flow when stress is applied to the bond at theinterface. PSAs exhibit viscoelastic (viscous and elastic) properties,both of which may be used for creating proper bonding.

Currently, PSAs are mainly fabricated from soft, viscoelastic polymermaterials (e.g., coatings), which are used either independently or inconjunction with a backing material, such as a stiff film or cloth. Tocontrol the level of adhesion, PSAs alter their bulk properties byrelying upon a complex formulation of both elastic and viscoelasticcomponents to delicately balance the ability of a material to form aninterface (or “wet a surface”) and the resistance to separation once theinterface is formed. (Benedek, et al. Eds. 2009 Handbook of PressureSensitive Adhesives and Products Series, CRC Press: Boca Raton; Pocius,2002, Adhesion and Adhesives Technology: An Introduction, Hanser Publ.:Munich; Crosby, et al. 1999 J. Poly. Sci. Part B: Polym. Phys. 37, 24,3455-3472; Creton, 2003 “Materials Science of Adhesives: How to BondThings Together.” MRS Bulletin 28, 6, 419-421; Creton, 2003“Pressure-sensitive adhesives: An introductory course.” MRS Bulletin 28,6, 434-439; Creton, et al. 2007 “Sticky Feet: From Animals toMaterials”, MRS Bulletin 32, 6, all pages; Chan, et al. 2007 “DesigningModel Systems for Enhanced Adhesion.” MRS Bulletin 32, 6, 496-503;Boesel, et al. 2010 Advanced Materials 22, 19, 2125-2137.)

Among the various aspects of PSA designs, three factors are typicallyrelevant and emphasized: (1) Conventional PSAs are viscoelastic to allowthe polymer coating to conform easily with rough a surface whiledissipating mechanical energy (i.e., pressure) that is required forconformality; (2) A measure for strong PSA materials is tack energy,which is the total energy dissipated during the separation of aPSA/substrate interface; (3) High tack PSAs are typically not conduciveto multiple loading applications due to the irreversible (i.e.inelastic) materials processes that are used to produce high levels oftack.

To develop adhesive material systems that overcome some of thedisadvantages of conventional PSAs, much research has focused on thedevelopment of gecko-like adhesive systems. Some key attributes of bothconventional PSAs and ideal gecko-like adhesives are provided in thefollowing table:

Conventional Ideal “Gecko-Like” Property PSA Adhesive Max Shear StressHigh High Max Normal Stress High High Peel Resistance High Low (afterreaching critical peel angle) Energy of Separation High LowReversibility Limited to None High Time/Temp Dependence High UnknownImpact of Fouling High Limited

Additionally, the adhesive surface of geckos, and similar examples inNature, is commonly described as “dry”, i.e., that adhesion does notrely upon liquid interactions, liquid-to-solid transitions like anepoxy, nor does the adhesive surface feel “tacky” to the touch like aconventional viscoelastic adhesive. Although such attributes are knownand displayed in Nature, the primary design factors or mechanisms thatpermit good control of properties is not known and remains the subjectof current research projects worldwide. To our knowledge, thedevelopment of a synthetic analog to a gecko-like adhesive has not beendemonstrated, in particular one that could be used on macroscopic lengthscales.

There is a significant and ongoing need for designs, systems, devices,materials and related fabrication methods for adhesive systems that canbe used to easily attach and support high capacity loads, yet providesimple, non-damaging release and repeated use while being cost-effectiveto produce.

SUMMARY OF THE INVENTION

The invention provides unique releasable adhesive devices that areuseful for attachment to various surfaces and allow significant weightbearing. The materials, designs, systems, and related methods offabrication and production disclosed herein provide adhesive devicesthat have high load capacity, are reusable, easy release and suitablefor extended and repeated use. Attachment pads disclosed herein can bedesigned, for example, to fit a number of applications ranging fromhousehold weight-bearing shelves and holders, components for indoor andoutdoor climbing devices, components for transportation, athleticequipment, labels and advertising posts, automobile interior trims,permanent or reversible fasteners, as well as instruments and devicesfor industrial, commercial, medical or military settings.

In one aspect, the invention generally relates to a releasable,surface-adhesive device. The device includes an adhesive pad and atether component attached to the adhesive pad. The adhesive padincludes: a planar backing layer having high in-plane stiffness; and aplanar layer of an elastic material having an adhesive surface on atleast one side for adhering to a target surface, wherein the elasticmaterial is impregnated onto the backing layer on at least the sideopposing the adhesive surface. In certain preferred embodiment, thedevice further comprises a holding component for load bearing. Theholding component being attachable to the tether component forconnecting an object to the device.

In another aspect, the invention generally relates to a releasable,surface-adhesive device. The device includes: a planar layer comprisingan elastic material and having on one side an adhesive surface foradhering to a target surface and on the other side a backing layerhaving high in-plane stiffness, wherein the elastic materialimpregnating into the fabric backing layer; and a holding componentattachable to the backing layer for connecting an object to the device.A portion of the backing layer extends beyond the layer of the elasticmaterial to form an area of the backing layer un-impregnated with theelastic material, and the holding component attaches to the backinglayer at such area of the backing layer un-impregnated with the elasticmaterial.

In yet another aspect, the invention generally relates to a releasable,reusable surface-adhesive device. The device includes an adhesive padthat has a planar layer of an elastic material having an adhesivesurface on one side for adhering to a target surface; and a planarbacking layer having high in-plane stiffness, wherein the backing layeris impregnated onto the layer of the elastic material on the sideopposing the smooth adhesive surface. The device further includes atether attached to the adhesive pad substantially at the center of theadhesive pad and allowing adjustment of the angle between the tether andthe adhesive pad from about 0° to about 359°.

In yet another aspect, the invention generally relates to a releasable,surface-adhesive device. The device includes an adhesive pad, which hasa planar layer of an elastic material having a microscopically smooth orpatterned adhesive surface on one side for adhering to a target surface;and a planar backing layer having high in-plane stiffness, wherein thebacking layer is impregnated onto the layer of the elastic material onthe side opposing the smooth adhesive surface. The device furtherincludes a tether component attached to the adhesive pad; and a holdingcomponent for load bearing. The holding component is attachable to thetether component for connecting an object to the device.

In yet another aspect, the invention generally relates to a method forreleasably holding a weight on a surface. The method includes: (a)providing a releasable, surface-adhesive device having an adhesive padcomprising a planar layer of an elastic material having amicroscopically smooth adhesive surface on one side for adhering to atarget surface; and a planar fabric backing layer having high in-planestiffness, wherein the fabric backing layer is impregnated onto thelayer of the elastic material on the side opposing the smooth surface; afabric tether attached to the adhesive pad; and a holding component forload bearing attachable to the fabric tether for connecting an object tothe device; and (b) attaching the weight to the holding component.

In yet another aspect, the invention relates to a method for making areleasable, surface-adhesive device. The method includes: (a) providingan elastic material; (b) providing a fabric backing sheet; (c) curingthe elastic material to impregnate the elastic material into at least aportion of the fabric backing sheet to form a pad having a layer of theelastic material with a smooth adhesive surface; (d) attaching aweight-holding component to the fabric backing sheet. The elasticmaterial has an elasticity from about 0.05 MPa to about 50 MPa, and thelayer of the elastic material has a thickness from about 0.0001 cm toabout 0.1 cm.

In yet another aspect, the invention generally relates to a method formaking a releasable, surface-adhesive device. The method includes: (a)providing a fabric backing sheet, on one side of which is placed asubstrate layer; (b) providing, on the other side of the fabric backingsheet, a spacer-defined molding area; (c) adding an elastic materialinto the spacer-defined molding area of the fabric backing sheet; (d)covering the elastic material with a top cover having a microscopicallysmooth or patterned surface; (e) applying pressure against the top covercausing an intimate interface between the top pad and the elasticmaterial; (f) curing the elastic material to impregnate the elasticmaterial into at least a portion of the fabric backing sheet to form apad having a layer of the elastic material with a microscopically smoothor patterned adhesive surface; and (g) attaching a weight-holdingcomponent to the fabric backing sheet. The elastic material has anelasticity from about 0.05 MPa to about 50 MPa, and the layer of theelastic material has a thickness from about 0.0001 cm to about 0.1 cm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of an exemplary embodiment of theinvention.

FIG. 2 shows certain design factors and schematic illustrations.

FIG. 3 shows a schematic illustration of an exemplary fabricationprocess.

FIG. 4 shows schematic illustrations of various embodiments of theinvention for the pad-tether connection.

FIG. 5 shows exemplary force vs. displacement measurements forcharacterizing maximum force supported under pure shear loading for“T-pad” structures.

FIG. 6 shows exemplary maximum shear force supported for various “T-pad”configurations, live geckos, and non-fabric backed polymer coatings as afunction of the square root of interfacial area normalized by in-planecompliance.

FIG. 7 shows exemplary failure force per unit width as a function ofpeel angle for various “T-pad” configurations.

FIG. 8 shows certain examples of complete “T-Pad” structures supportingloads on various surfaces.

FIG. 9 schematically illustrates an exemplary embodiment of fabricationof adhesive pads according to the invention.

FIG. 10 shows exemplary images of fabric adhesives. (A) A nylon fabricPDMS adhesive, (B) A carbon fiber/Kevlar plain weave fabric PDMSadhesive, and (C) a unidirectional carbon fiber polyurethane adhesive.

FIG. 11 shows exemplary plot of modulus against frequency for an exampleof polyurethane.

FIG. 12 shows schematic illustrations of an embodiment of the moldingtechnique for fabricating an adhesive pad according to the invention.

FIG. 13 shows exemplary results of a controlled displacement test (loadplotted against extension).

FIG. 14 shows exemplary results of the repeatability of a polyurethaneadhesive pad undergoing cyclic loading.

FIG. 15 shows static load test performed with polyurethane adhesivesholding 136 kg.

FIG. 16 shows exemplary load data from polyurethane adhesives with avariety of substrates.

FIG. 17 shows the static load test performed on (A) a center loaded PDMSadhesive pad holding a 42″ flat panel television and (B) a center loadedpolyurethane adhesive pad holding a hooded sweatshirt on drywall.

FIG. 18 (A) shows schematic illustrations of the loading angledependence for the high capacity and easy release adhesive pads. (B)Shows exemplary results of the angle dependence of the center loaded padcompared to a single slab adhesive pad, where the center loaded padmaintains a high failure force throughout various loading angles, whilestill allowing for easy release.

DETAILED DESCRIPTION OF THE INVENTION

The invention is based in part on the discovery of novel designs,systems, devices, and associated materials and methods of fabrication,which enable large contact surfaces, high-load capacity, easy release,extended use, and repeated use. More particularly, the present inventionprovides a unique, previously unknown approach to adhesive systems,which is distinctive from conventional PSA systems and the more recentlyexplored gecko-like adhesives.

The invention differs from prior art in the field of PSAs at least inthat the present invention does not rely on viscoelastic properties toachieve performance controls, as do PSAs. Designs and systems of theinvention allow separation time and energy to be minimized, whilemaintaining the ability to support extremely high-weight loads. Largeareas of interfacial contact can be designed through the combinedproperties of the soft elastic layer and the “draping” characteristicsof a fabric layer. Furthermore, the elastic design provides a mechanismfor repeated attachment and separation cycles without degradation in theload bearing capacity of the adhesive interface.

In contrast to prior art in the development of gecko-type adhesives, thedesigns, systems and methods disclosed herein do not require the use ofsurface fibrillar structures to achieve desired attributes. Followingthe principles disclosed herein, one may mimic the engineering design ofthe toe and leg structures of common examples in Nature, such as geckosin vertical climbing.

Other key differences between the present invention and the prior artrelate to, among others, the specific designation of rotational freedomat continuous junctions, specifications of stiffness in loadingdirection with low flexural rigidity perpendicular to surface of elasticmaterial, and the ability to achieve high capacity load support underboth normal and shear loading directions with near-zero required“pre-load” (referring to the amount of force that is required toestablish the adhesive/substrate interface for supporting a given load).

In one approach of the invention, the adhesive pad system disclosedherein employs a “dry” adhesive pad structure, sometimes referred to asa “T-pad”, an embodiment of which is schematically illustrated inFIG. 1. Properly designed, the T-pad device can support high loads undershear, normal, and multi-mode (i.e. peel) loadings while requiringminimal forces and energy for release (or separation) underspecifically-designed release strategies.

The basic structure of the adhesive device is referred to as the “pad”,which is subsequently connected to a tether (e.g., a synthetic fabrictether), which may be referred to as the “tendon”. The tether shouldmaintain high stiffness along the primary axis of loading. Theconnection between the tendon and the pad has pre-defined dimensions,orientation, and spatial location, according to particular needs, thatcan be modified to control the release strategy and provide toleratedbalance of shear and normal loading.

This approach represents a unique combination of adhesion attributes ofpolymer materials and integrated mechanical designs through properconservation of rotational freedom, low flexural modulus normal to theadhesive interface, and high stiffness in load bearing directions. Ascaling relationship has been developed by the inventors to provide aframework for understanding the adhesive performance of the materialsdevices over a range of size scales and geometries (FIG. 2). Thisscaling relationship suggests that the adhesive capacity (F_(C)) of aninterface is governed by three simple parameters, which are dependent onboth the geometry and material properties of the interface. To designreversible adhesives which can adhere to various substrates, theinterfacial interactions (G_(C)) should rely upon non-specific van derWaals forces, rendering G_(C) an ineffective control parameter.Therefore, to scale F_(C) for adhesive materials the material systemmust not just rely on area on contact (A) or the system compliance (C)but must develop attributes that increase the A/C ratio. This presents achallenge; materials must be soft to increase true contact but stiff toachieve high loads. Soft materials are able to create large-scalecontact but have a high compliance when loaded, while stiff materialsare unable to create extensive contact; both cases result in a nulleffect on the A/C ratio. The current invention provides a mechanism formaximizing A/C, and most importantly, tuning this governing parameterfor different applications. As schematically illustrated in FIG. 3, anefficient and effective fabrication method may be used to fabricate theT-pad. The method involves integrating a thin layer of an elasticelastomer into a surface of a fabric.

The tether (tendon) can be connected to the pad through any suitablemethods, such as conventional sewing, stitching, or gluing, which allowseasy control of dimensional, orientational, and spatial location of theattachment. The attachment should provide sufficient load sharing andload bearing capacity, which can be controlled through the stitchingpattern, width, and length. Appropriate stitching patterns includestraight stitching, zigzag stitching, multi zigzag stitch, satinstitching, honeycomb stitching, ladder stitch, double overlock stitch,and criss-cross stitching.

For example, a particularly advantageous tether-pad connection is astraight-line stitch that is centered on the one axis of the pad andextends to a length of approximately ⅔ the chord length perpendicularthe second pad axis. The tether-pad connection should maintainrotational freedom while maintaining high stiffness in the direction ofloading. The tether-pad connection should preferably maintain equal loadsharing along the entire length of the connection. At a distancesufficiently far from the tether-pad connection, the tether isintegrated into a load bearing material that has high flexural rigidityand in-plane stiffness. This rigid terminal material is sometimesreferred to as the “skeleton” (the “holding component”). The connectionbetween the tether-skeleton should preferably be continuous to ensureequal load sharing along the length of the connection.

The invention includes the designs where one T-pad structure can actindependently or in conjunction with an array of T-pad structures orunits (referred to as a “T-surface”), which may be mounted withrotationally-free joints to a supporting substrate that can be rigid inone or more directions, for example. For certain applications, e.g., alarge weight bearing shelf, multiple attachment points for the tether tothe adhesive pad may also be employed.

FIG. 4 shows schematic illustrations of various T-pad configurations forthe tether-pad connection. Skeleton connection is not shown. A singleslab connection constitutes a continuous adhesive pad and supportbacking, which can then be divided into a larger number of discreteadhesive pads and support backings in which multiple tendons are used tocreate different configurations (e.g., a gradient length seriesconfiguration). The off edge tendon connection and center loaded padconfigurations constitute an adhesive pad and support backing where aplanar tether attached to the adhesive pad substantially at the center,where the length of the attachment can be equal to the width in the caseof the T-pad or some fraction or the width in the case of the centerloaded pad. In both cases the tether attached to the adhesive pad allowsfor adjustment of the angle between the planar tether and the adhesivepad from about 0° to about 359°.

Elastic materials that may be used in the adhesive pads includesiloxane-based elastomers, urethane-based elastomers, and acrylate-basedelastomers. Polydimethylsiloxane (PDMS) belongs to a group of polymericorganosilicon compounds that are commonly referred to as silicones.PDMS, widely used silicon-based organic polymer, has preferredrheological (or flow) properties. PDMS is generally inert, non-toxic andnon-flammable.

Other elastic materials that may be used in the adhesive pads includepolyurethanes, which are polymers of organic units covalently joined byurethane (carbamate) links.

A urethane linkage is produced by reacting an isocyanate group, —N═C═Owith a hydroxyl group, —OH. Polyurethanes are produced by thepolyaddition reaction of a polyisocyanate with a polyalcohol (polyol) inthe presence of a catalyst and other additives. In this case, apolyisocyanate is a molecule with two or more isocyanate functionalgroups, R—(N═C═O)_(n)≧2 and a polyol is a molecule with two or morehydroxyl functional groups, R′—(OH)_(n)≧2. The reaction product is apolymer containing the urethane linkage, —RNHCOOR′—. Examples ofpolyurethane monomers (“pre-polymers”) includes hydroxyl endedmolecules, such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, or bisphenol A (hydroxyl-containing monomers) andan aliphatic or aromatic based isocyanate, such as methylene diphenyldiisocyanate, toluene diphenyl diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate, or a polyisocyanate resulting from thecombination of multiple of these monomers (for example, three moleculesof methylene diphenyl diisocyanate form a trimer which contains threeisocyanate functional groups).

In one aspect, the invention generally relates to a releasable,surface-adhesive device. The device includes an adhesive pad and atether component attached to the adhesive pad. The adhesive padincludes: a planar backing layer having high in-plane stiffness; and aplanar layer of an elastic material having an adhesive surface on atleast one side for adhering to a target surface, wherein the elasticmaterial is impregnated onto the backing layer on at least the sideopposing the adhesive surface. In certain preferred embodiment, thedevice further comprises a holding component for load bearing. Theholding component being attachable to the tether component forconnecting an object to the device.

It is noted that the term “backing”, as used herein, includes but is notlimited to the situation where the referred to layer or material is theback (or the last) layer of the device structure. According to thisinvention, a backing layer may be an interior layer or component of astructural arrangement.

In certain embodiments, the adhesive pad includes: a planar layer of anelastic material having an adhesive surface on one side for adhering toa target surface; and

a planar backing layer having high in-plane stiffness, wherein thebacking layer is impregnated onto the layer of the elastic material onthe side opposing the adhesive surface.

In certain embodiments, the adhesive surface is microscopically smooth.In certain embodiments, the adhesive surface is microscopicallypatterned.

In certain embodiments, the backing layer is a fabric backing layer.

In certain embodiments, the elastic material has a adhesive surface areafrom about 0.01 cm² to about 1,000 cm² (e.g., about 0.01 cm², 0.05 cm²,0.1 cm², 0.5 cm², 1 cm², 2 cm², 5 cm², 10 cm², 20 cm², 50 cm², 100 cm²,200 cm², 500 cm², 1,000 cm²) and a substantially uniform thickness fromabout 0.001 cm to about 0.1 cm. In certain embodiments, the planar layerof the elastic material has a smooth adhesive surface area of greaterthan about 0.01 cm² and has a substantially uniform thickness of lessthan about 0.001 cm. In certain embodiments, the planar layer of theelastic material has a smooth adhesive surface area of greater thanabout 0.05 cm² and has a substantially uniform thickness of less thanabout 0.005 cm. In certain embodiments, the planar layer of the elasticmaterial has a smooth adhesive surface area of greater than about 0.1cm² and has a substantially uniform thickness of less than about 0.01cm. In certain embodiments, the planar layer of the elastic material hasa smooth adhesive surface area of greater than about 0.2 cm² and has asubstantially uniform thickness of less than about 0.5 cm. In certainembodiments, the planar layer of the elastic material has a smoothadhesive surface area of greater than about 0.5 cm² and has asubstantially uniform thickness of less than about 0.2 cm. In certainembodiments, the planar layer of the elastic material has a smoothadhesive surface area of greater than about 1.0 cm² and has asubstantially uniform thickness of less than about 0.1 cm. In certainembodiments, the planar layer of the elastic material has a smoothadhesive surface area of greater than about 5.0 cm² and has asubstantially uniform thickness of less than about 0.05 cm. In certainembodiments, the planar layer of the elastic material has a smoothadhesive surface area of greater than about 10 cm² and has asubstantially uniform thickness of less than about 0.02 cm. In certainembodiments, the planar layer of the elastic material has a smoothadhesive surface area of greater than about 100 cm² and has asubstantially uniform thickness of less than about 0.01 cm. In certainembodiments, the planar layer of the elastic material has a smoothadhesive surface area from about 10 cm² to about 100 cm² and has asubstantially uniform thickness from about 0.01 cm to about 0.05 cm. Incertain embodiments, the planar layer of the elastic material has asmooth adhesive surface area from about 1,000 cm² to about 100 cm² andhas a substantially uniform thickness from about 0.5 cm to about 0.05cm.

In certain embodiments, the elastic material has an elasticity fromabout 0.05 MPa to about 50 MPa. In certain embodiments, the elasticmaterial has an elasticity from about 0.05 MPa to about 30 MPa. Incertain embodiments, the elastic material has an elasticity from about0.05 MPa to about 10 MPa. In certain embodiments, the elastic materialhas an elasticity from about 1 MPa to about 50 MPa. In certainembodiments, the elastic material has an elasticity from about 1 MPa toabout 30 MPa. In certain embodiments, the elastic material has anelasticity from about 1 MPa to about 10 MPa.

In certain embodiments, the elastic material includes a siloxane-basedelastomer. In certain embodiments, the elastic material includes aurethane-based elastomer. In certain embodiments, the elastic materialincludes an acrylate-based elastomers. In certain preferred embodiments,the elastic material includes polydimethylsiloxane (PDMS). In certainembodiments, the elastic material includes a polyurethane, for example,prepared from polymerization of a hydroxyl ended polyethylene glycolwith an aliphatic or aromatic based polyisocyanate. Any suitablematerials may be used including styrene-butadiene-styrene elastomers andother thermoreversible block copolymer elastomers; liquid crystallineelastomers; natural rubber.

In certain embodiments, the material of the fabric backing layerincludes a natural fabric material or a synthetic fabric material. Incertain embodiments, the material of the fabric backing layer includes anatural fabric material such as cotton, hemp, wool, silk, bamboo string,cellulose, jute or pina. In certain embodiments, the material of thefabric backing layer includes a synthetic fabric of polyester, spandex,nylon, carbon fiber, polyaramid, carbon fiber polyaramid hybrid, carbonfiber basalt hybrid, fiberglass, or fiberglass hybrid. In certainpreferred embodiments, the material of the fabric backing layercomprises a material selected from the group consisting of nylon, carbonfiber, polyaramid, carbon fiber and polyaramid hybrid.

In certain embodiments, the device has an adhesive surface area of 100cm² or greater and capable of bearing a weight or at least 1200N per 100cm² of adhesive surface area. In certain embodiments, the device has anadhesive surface area of 100 cm² or greater and capable of bearing aweight of at least 3150 N per 100 cm² of adhesive surface area. Incertain embodiments, the device has an adhesive surface area of 1 cm² orgreater and capable of bearing a weight of at least 12.0 N per 1 cm² ofadhesive surface area. In certain embodiments, the device has anadhesive surface area of 1 cm² or greater and capable of bearing aweight of at least 31.5 N per 1 cm² of adhesive surface area.

In certain embodiments, the tether is a fabric material, for example,selected from synthetic fabrics like polyester, spandex, nylon, carbonfiber, polyaramid, carbon fiber polyaramid hybrid, carbon fiber basalthybrid, fiberglass, carbon fiber, or fiberglass hybrid, and naturalfabrics including cotton, hemp, wool, silk, bamboo string, cellulose,jute, and pina. In certain embodiments, the tether is a non-fabricmaterial, for example, selected from leather, metal sheets, plasticsheets, or non-woven textiles. In some embodiments, the material is madefrom chain-link meshes.

In another aspect, the invention generally relates to a releasable,surface-adhesive device. The device includes: a planar layer comprisingan elastic material and having on one side an adhesive surface foradhering to a target surface and on the other side a backing layerhaving high in-plane stiffness, wherein the elastic materialimpregnating into the backing layer; and a holding component attachableto the backing layer for connecting an object to the device. A portionof the backing layer extends beyond the layer of the elastic material toform an area of the backing layer un-impregnated with the elasticmaterial, and the holding component attaches to the backing layer atsuch area of the backing layer un-impregnated with the elastic material.

In certain embodiment, the elastic material can extend beyond the fabriclayer on the “back side” of the pad. This design may aid theestablishment of uniform contact without sacrificing the stiffness ofthe device that is directly related to the force capacity of theadhesive device.

In yet another aspect, the invention generally relates to a releasable,reusable surface-adhesive device. The device includes an adhesive padthat has: a planar layer of an elastic material having an adhesivesurface on one side for adhering to a target surface; and a planarbacking layer having high in-plane stiffness, wherein the backing layeris impregnated onto the layer of the elastic material on the sideopposing the smooth adhesive surface. The device further includes atether attached to the adhesive pad substantially at the center of theadhesive pad and allowing adjustment of the angle between the planartether and the adhesive pad from about 0° to about 359°.

In certain embodiments, the adjustable angle between the tether and theadhesive pad range from about 0° to about 90°, for example, 15°, 30°,45°, or 60°. In certain other embodiments, the adjustable angle betweenthe tether and the adhesive pad range from about 90° to about 120°, forexample, 95°, 110°, 110°, or 115°. In certain other embodiments, theadjustable angle between the tether and the adhesive pad range fromabout 120° to about 360°, for example, 150°, 180°, 210°, 270° or 300°.

In yet another aspect, the invention generally relates to a releasable,surface-adhesive device. The device includes an adhesive pad, which hasa planar layer of an elastic material having a microscopically smooth orpatterned adhesive surface on one side for adhering to a target surface;and a planar fabric backing layer having high in-plane stiffness,wherein the backing layer is impregnated onto the layer of the elasticmaterial on the side opposing the adhesive surface. The device furtherincludes a tether component attached to the adhesive pad; and a holdingcomponent for load bearing, the holding component being attachable tothe tether component for connecting an object to the device.

In yet another aspect, the invention generally relates to a method forreleasably holding a weight on a surface. The method includes: (a)providing a releasable, surface-adhesive device having an adhesive padcomprising a planar layer of an elastic material having amicroscopically smooth adhesive surface on one side for adhering to atarget surface; and a planar fabric backing layer having high in-planestiffness, wherein the fabric backing layer is impregnated onto thelayer of the elastic material on the side opposing the smooth surface; afabric tether attached to the adhesive pad; and a holding component forload bearing attachable to the fabric tether for connecting an object tothe device; and (b) attaching the weight to the holding component.

In yet another aspect, the invention relates to a method for making areleasable, surface-adhesive device. The method includes: (a) providingan elastic material; (b) providing a fabric backing sheet; (c) curingthe elastic material to impregnate the elastic material into at least aportion of the fabric backing sheet to form a pad having a layer of theelastic material with a smooth adhesive surface; (d) attaching aweight-holding component to the fabric backing sheet. The elasticmaterial has an elasticity from about 0.05 MPa to about 50 MPa, and thelayer of the elastic material has a thickness from about 0.0001 cm toabout 0.1 cm.

In yet another aspect, the invention generally relates to a method formaking a releasable, surface-adhesive device. The method includes: (a)providing a fabric backing sheet, on one side of which is placed asubstrate layer; (b) providing, on the other side of the fabric backingsheet, a spacer-defined molding area; (c) adding an elastic materialinto the spacer-defined molding area of the fabric backing sheet; (d)covering the elastic material with a top cover having a microscopicallysmooth or patterned surface; (e) applying pressure against the top covercausing an intimate interface between the top pad and the elasticmaterial; (f) curing the elastic material to impregnate the elasticmaterial into at least a portion of the fabric backing sheet to form apad having a layer of the elastic material with a microscopically smoothor patterned adhesive surface; and (g) attaching a weight-holdingcomponent to the fabric backing sheet. The elastic material has anelasticity from about 0.05 MPa to about 50 MPa, and the layer of theelastic material has a thickness from about 0.0001 cm to about 0.1 cm.

In certain embodiments, the ratio of storage to loss elastic moduli isat least greater than about 10 (e.g., greater than 15, 20, or 50) at theoperating temperature of interest.

The layer of the elastic material may have any size and shape as aparticular application requires, for example, it may have asubstantially circular outer boundary, a substantially rectangular outerboundary, a substantially elliptical outer boundary, or a substantiallyirregular outer boundary.

As stated herein, in some embodiments, the layer of an elastic materialincludes two, three, four or more separate smaller elastic materiallayer units or structures. The target surface may be any suitablesurfaces, including that of glass, metal, wood, plastic, paper,cardboard, or concrete.

Repeated attachment and release of loads has been demonstrated underpure shear and normal loading directions, as well as controlled peelangles, with magnitudes of performance unmatched by any existingproducts to our knowledge. For example, an experimental device was ableto support loads as great as 707 pounds with a 16 square inch T-pad (44psi), with minimal force required for detachment, a performance repeatedon the same pad for numerous cycles with negligible degradation inperformance. Additionally, an adhesive pad structure can be easilycleaned with soap and water or a particle transfer material, such as aviscoelastic, acrylic tape. The release mechanism may be designedaccording to the principles disclosed herein to fit particularapplications.

The integrated adhesive pad approach of the invention provides a robustplatform for a wide-variety of applications. For example, thesestructures can be used to support shelving for books, displays, andelectronic appliances (televisions, computers, stereos, monitors,screens); hanging structures; auto trims; among others. Furthermore, thecurrent designs can be used to facilitate climbing on vertical surfacesor overhangs that are made from a variety of materials, such as glass,metal, wood, and drywall.

EXAMPLES Force vs. Displacement Tests

FIG. 5 shows exemplary force vs. displacement measurements forcharacterizing maximum force supported under pure shear loading forT-pad structures. (Fabric backing varied. All results were for 16 in²pad with varying thicknesses labeled as ‘t’ in the legend.) Theexperiments were run on an Instron testing machine in a single lab jointgeometry where attachment was made between the adhesive pad and a smoothclean glass substrate. The extension was controlled to be 10 mm/min andthe load was measured throughout the test. The maximum load correspondsto the critical failure load, which varies depending on fabric backingas shown.

FIG. 6 shows maximum shear force supported for various T-padconfigurations, natural data (which includes live geckos and variousattachment devices for geckos, beetles, spiders, crickets, and flys),and non-fabric backed polymer coatings as a function of the square rootof interfacial area normalized by in-plane compliance. Trend linefollows predicted scaling relationship demonstrating ability topredictably tune maximum shear force performance.

Failure Force Tests

FIG. 7 shows failure force per unit width as a function of peel anglefor different T-pad configurations (total contact area for each adhesivepad is 10.8 cm², and the center loaded pad connection is ⅔ the width).Demonstrating ability to tune critical angle for easy release. Peelexperiments were conducted on an Instron 5500 R on clean glass at 10mm/min, and the angle between the applied load and substrate was variedbetween 0° and 90°.

FIG. 8 shows some simple examples of complete T-Pad structure to supportloads on various surfaces. The same nylon fabric PDMS adhesive (A=16 in²with thickness of 1 mm) pad structure is used in all examples.

Fabrication of PDMS Adhesive Pads

FIG. 9 schematically illustrates an embodiment of fabrication of PDMSadhesive pads. (A) To prepare PDMS adhesives, molds were fabricatedusing glass slides. Uncured, degassed PDMS oligomer and curing agent(Dow Corning Sylgard 184™) 10:1 ratio (w/w) were poured into the mold.The mold was constructed such that its thickness was greater than theroughness of the fabric, which allowed for a smooth surface finish onthe adhesive after fabrication. After the degassed PDMS was poured andallowed to spread into the mold, a 6-8 minute pre-cure at 70° C. wasperformed before the application of the fabric to help support thefabric during the subsequent cure. (B) Fabric was then placed over themold allowing the uncured PDMS to impregnate the fabric, and was thencured at room temperature for 3 days. The fabric consisted of a singlepiece that was cut so that the width overlaps the edges of the mold toprovide support, and the length was sufficiently long to cover the moldand create the “tendon” structure. The tendon can also be impregnatedwith elastomer to provide for equal load sharing.

In another embodiment, the fabric was designed to be a center loadedpad, such that a fabric tendon was stitched to the center of theadhesive pad fabric. In this scheme, the tendon structure was alsoimpregnated with PDMS to ensure that the fabric did not unravel duringsubsequent load application. This was achieved by placing one separatorsheet between the tendon and the adhesive pad, then spreading PDMSacross the tendon, followed by placing a capping separator sheet on topof the impregnated tendon. (C) After the PDMS was cured, the fabricadhesive was removed from the mold and mechanically cut to size. A rigidmount (“skeleton”) consisting of 2⅛″ thick plastic sheets were attachedto the bottom of the tendon using cyanoacrylate adhesive, which was thenallowed to cure for 6 hours.

FIG. 10 shows exemplary images of: (A) a photograph of a nylon fabricPDMS adhesive, (B) a carbon fiber/Kevlar plain weave fabric PDMSadhesive, and (C) an unidirectional carbon fiber polyurethane adhesive.The center column shows a scanning electron microscope (SEM) image ofthe side profile with the adhesive side facing up, and the right columnshows the smooth adhesive surface. Scale bars in the optical photographsare 5 cm, and all scale bars in the SEM images are 500 μm.

Polyurethane Adhesives

Polyurethane adhesives have been synthesized by adding 1:1 ratio offunctional groups of hydroxyl ended polyethylene glycol, polypropyleneglycol, and/or polytetramethylene glycol, with either aliphatic oraromatic based polyisocyanates. Commercial kits of polyurethanes havealso been utilized in this application.

FIG. 11 shows modulus is plotted against frequency for an example ofpolyurethane. The storage modulus is about an order of magnitude greaterthan the loss modulus, showing that the sample has predominantlysolid-like, elastic properties. The modulus also varies little over twoorders of magnitude in frequency.

FIG. 12 schematically illustrates an embodiment of the molding techniqueby which to form a pad with polyurethane. On top of apolytetrafluoroethylene substrate fiber was placed for the adhesivebacking layer. A low-density polyethylene (LDPE) spacer was placed ontop of the fiber that allows for controlling polyurethane (PU)thickness, and uncured PU prepolymer was poured into the mold. Apolydimethylsiloxane pad was then placed on top with a glass plate, andfinally the system was weighted with a 45 pound weight.

Utilizing this molding technique, a smooth adhesive surface (utilizing asmooth PDMS top layer), or surface features (utilizing a patterned PDMStop layer) can be achieved. The thickness of the adhesive can be changedby modifying the thickness of the LDPE spacer. This method may also bealtered to work using a doctor blade system, which would allow for massproduction of adhesive pads.

Loading Tests

Sample adhesive pads were tested using an Instron controlleddisplacement test. Mechanical grips were attached to an Instron 5500 R,with a pane of glass attached to the grip on the crosshead, and theadhesive pad secured to the bottom grip. The adhesive pad was thenadhered to the glass, and a displacement of 10 mm/min was used until theadhesive detached from the glass. This test was repeated multiple timesto determine the average failure force, and prove reusability. FIG. 13shows that there is an initial loading regime, and by finding the slopeof this line one can find the stiffness of the adhesive system thatcontrols the total capacity of the adhesive. The stiffness (andtherefore, total capacity) for these polyurethane adhesives is greaterthan previously recorded values of stiffness. At the peak of this curveis the total capacity (˜2950 N for this sample). After this peak theadhesive releases from the glass, resulting in a drop in the registeredload. This test can be repeated, and we have shown good reproducibilityover 100 cycles of testing (FIG. 14).

Static load testing was also performed on these polyurethane adhesives.A bar containing 136 kg of mass was connected via chain to an adhesivepad, and was also supported by a pulley system. Using the pulley system,the weights were raised until the adhesive could be adhered to the glassadherend setup. The pulley system was then lowered until the total loadwas supported by the adhesive. Certain results of such tests are shownin FIG. 15, wherein the tests were performed by holding 136 kg on glasssurfaces.

As shown in FIG. 16, these polyurethane adhesives can be used on avariety of substrates. These results were performed similarly toprevious loading tests, however, the glass pane was either replaced witha new material, or a new material was adhered to the surface of a glasspane. FIG. 17 shows the static load test performed on (A) a 16 in²center loaded PDMS adhesive pad holding a 42″ flat panel television and(B) a center loaded polyurethane adhesive pad holding a hoodedsweatshirt on drywall. FIG. 18 (A) shows schematic illustrations of theloading angle dependence for the high capacity and easy release adhesivepads. (B) Shows results of the angle dependence of the center loaded padcompared to a single slab adhesive pad, where the center loaded padmaintains a high failure force throughout various loading angles, whilestill allowing for easy release.

INCORPORATION BY REFERENCE

References and citations to other documents, such as patents, patentapplications, patent publications, journals, books, papers, webcontents, have been made in this disclosure. All such documents arehereby incorporated herein by reference in their entirety for allpurposes.

EQUIVALENTS

The representative examples are intended to help illustrate theinvention, and are not intended to, nor should they be construed to,limit the scope of the invention. Indeed, various modifications of theinvention and many further embodiments thereof, in addition to thoseshown and described herein, will become apparent to those skilled in theart from the full contents of this document, including the examples andthe references to the scientific and patent literature included herein.The examples contain important additional information, exemplificationand guidance that can be adapted to the practice of this invention inits various embodiments and equivalents thereof.

What is claimed is:
 1. A releasable, surface-adhesive device,comprising: an adhesive pad, comprising: a planar backing layer havinghigh in-plane stiffness; a planar layer of an elastic material having anadhesive surface on at least one side for adhering to a target surface,wherein the elastic material is impregnated onto the backing layer on atleast the side opposing the adhesive surface; and a tether componentattached to the adhesive pad.
 2. The releasable, surface-adhesive deviceof claim 1, further comprises a holding component for load bearing, theholding component being attachable to the tether component forconnecting an object to the device.
 3. The releasable, surface-adhesivedevice of claim 1, wherein the adhesive pad comprises: a planar layer ofan elastic material having an adhesive surface on one side for adheringto a target surface; and a planar backing layer having high in-planestiffness, wherein the backing layer is impregnated onto the layer ofthe elastic material on the side opposing the adhesive surface.
 4. Thereleasable, surface-adhesive device of claim 1, wherein the adhesivesurface is microscopically smooth.
 5. The releasable, surface-adhesivedevice of claim 1, wherein the adhesive surface is microscopicallypatterned.
 6. The releasable, surface-adhesive device of claim 1,wherein the backing layer is a fabric backing layer.
 7. The releasable,surface-adhesive device of claim 4, wherein the planar layer of theelastic material has a smooth adhesive surface area of greater thanabout 0.01 cm² and has a substantially uniform thickness of less thanabout 0.0001 cm.
 8. The releasable, surface-adhesive device of claim 4,wherein the planar layer of the elastic material has a smooth adhesivesurface area of greater than about 0.2 cm² and has a substantiallyuniform thickness of less than about 0.5 cm. 9-14. (canceled)
 15. Thereleasable, surface-adhesive device of claim 6, wherein the elasticmaterial has an elasticity from about 0.05 MPa to about 50 MPa. 16-20.(canceled)
 21. The releasable, surface-adhesive device of claim 6,wherein the elastic material comprises a siloxane-based elastomer,urethane-based elastomer or a an acrylate-based elastomers. 22-25.(canceled)
 26. The releasable, surface-adhesive device of claim 6,wherein the material of the fabric backing layer comprises a naturalfabric material or a synthetic fabric material. 27-38. (canceled)
 39. Areleasable, surface-adhesive device, comprising: a planar layercomprising an elastic material, the planar layer having on one side anadhesive surface for adhering to a target surface and on the other sidea backing layer having high in-plane stiffness, wherein the elasticmaterial impregnating into the backing layer; and a holding componentattachable to the backing layer for connecting an object to the device,wherein a portion of the backing layer extends beyond the layer of theelastic material to form an area of the backing layer un-impregnatedwith the elastic material, and wherein the holding component attaches tothe backing layer at such area of the backing layer un-impregnated withthe elastic material.
 40. The releasable, surface-adhesive device ofclaim 39, wherein the adhesive surface is microscopically smooth. 41.The releasable, surface-adhesive device of claim 39, wherein theadhesive surface is microscopically patterned.
 42. The releasable,surface-adhesive device of claim 39, wherein the backing layer is afabric backing layer. 43-44. (canceled)
 45. The releasable,surface-adhesive device of claim 39, wherein the backing layer is anon-fabric backing layer. 46-47. (canceled)
 48. The releasable,surface-adhesive device of claim 39, wherein the layer of the elasticmaterial has a substantially circular outer boundary, a substantiallyrectangular outer boundary, a substantially irregular outer boundary ora substantially elliptical outer boundary. 49-51. (canceled)
 52. Thereleasable, surface-adhesive device of claim 39, wherein the layer of anelastic material comprises two or more separate smaller elastic materiallayer units. 53-58. (canceled)
 59. The releasable, surface-adhesivedevice of claim 40, wherein the planar layer of the elastic material hasa smooth adhesive surface area from about 0.01 cm² to about 1000 cm² andhas a substantially uniform thickness from about 0.001 cm to about 0.5cm. 60-77. (canceled)
 78. A releasable, reusable surface-adhesivedevice, comprising: an adhesive pad, comprising: a planar layer of anelastic material having an adhesive surface on one side for adhering toa target surface; and a planar backing layer having high in-planestiffness, wherein the backing layer is impregnated onto the layer ofthe elastic material on the side opposing the adhesive surface; a tetherattached to the adhesive pad substantially away from an edge at thecenter of the adhesive pad and allowing adjustment of the angle betweenthe tether and the adhesive pad from about 0° to about 359°. 79-130.(canceled)